Tom: How are your marks (grades) in Professor Smith's math class. Mona: They are very poor. Tom: What do you mean? Mona: Well, I earn a lot of C's [average work] and a lot of D's [below average work]. Tom: Don't feel bad. Mona: Why not? Tom: My grades are pathetic. Mona: What do you mean? Tom: Well, I almost always earn Fail's [no credit; repeat the work]. If I am lucky, sometimes I am able to earn one or two D's! Mona: That's pathetic! Tom: Yes, I know.

I just want to add to the above definition of Pathetic. Pathetic is an adjective. Pathetic: 1) marked by sorrow or melancholy 2) pitifully inferior or inadequate 3) absurd or laughable Anything can be described as pathetic. You say: This restaurant's service is pathetic. What this means is that the restaurant is doing such a poor job that it is arousing pity on itself. Pity means to feel sorry for. So you can say: This restaurant's service is so pathetic I actually feel sorry for them. So it is similar to saying it is poor, however you are saying it is so poor that its asking for pity. The 3) definition a little different. It essentially declares something that is absurd or laughable. You can say: That costume is pathetic. Here you are not saying the person is pathetic but the costume itself is. You can laugh while saying this.

Poor has a lot of meanings. In general, it either means lacking money (e.g. "poor people") or of bad quality ("poorly-made", "a poor performance", etc.). Pathetic, on the other hand, almost always refers to a person, and indicates that they're hopelessly awful. It's quite a nasty word. For example: "After he got fired, he's been reduced to begging on the street. How pathetic."